Electronic air cleaners have been in existence since the early 1960's. This field is now well developed and highly competitive. Due to the extent to which air cleaners have been developed, any improvement in cost or reliability to the air cleaner is significant.
Electronic air cleaner cells are constructed by joining air cleaner collector sections to end plates of the cells. Previously this was accomplished with screws from the end plates into the expansion tubes which support the collection plates. For smaller cells, a second method was used which consisted of passing a threaded rod through the first end plate, the collector expansion tube and, finally, the second end plate. A washer and nut was added to secure the assembly.
Air cleaners manufactured utilizing the method of placing a screw through the end plates into the cell expansion tubes have problems with screws coming loose due to variations in the required driving torque. The screws also come loose during handling or washing. At this time, this method is also expensive, as this method of manufacture requires the use of a human operator. Further, if the air cleaner cell were to be disassembled, the expansion tubes would be irreparable, requiring the air cleaner collection cell to be replaced. This is partially due to the fact that once the screws are threaded into the expansion tube, removed and replaced in the same expansion tube, the screw would not be able to achieve the same torque as when originally assembled.
The most significant problem created through use of the screws is torsional stress imparted on the cell expansion tubes by the screws. These torsional stresses reduce cell quality by warping the collection plates. The screw heads also tend to "walk" or shift on the end plate when tightened, placing lateral forces upon the collection plates, also warping the collection plates. This is significant as the air cleaner cell has every other collection plate charged to 4,075 volts dc. The remaining collection plates are grounded. Therefore, if the collection plates are warped, arcing may occur between the plates, reducing the effectiveness of the air cleaner.
The second prior art manner of assembly involves the use of a tie rod. This method of manufacture consists of passing a threaded rod through the first end plate, the cell expansion tube and, finally, through the second end plate. The tie rod was fastened in place by adding a washer and a nut. The use of a tie rod eliminates some of the problems with torsional stresses applied to the device. However, the tie rod is expensive, requires manual assembly and is also susceptible to the nuts loosening due to variations in the required driving torque, handling and washing. The tie rod is used primarily on small air cleaner cells due to the costs of the tie rod assembly. The screws impose such a severe torque upon the cell expansion tubes that screws are not practical with the smaller cells; the failure rate of the smaller cells manufactured with screws being too high. However, due to the cost of the tie rod assembly, the tie rods are not utilized where the failure rate of the air cleaner cells does not offset the costs.
Examples of electronic air cleaners can be found in U.S. Pat. No. 3,143,403 by Elmer H. Swensen and in U.S. Pat. No. 3,188,784 by K. M. Nodolf.